1. Field of the Disclosure
The disclosure relates generally to drive units or devices for use in downhole tools.
2. Description of the Related Art
Oil wells (also referred to as “wellbores” or “boreholes”) are drilled with a drill string that includes a tubular member having a drilling assembly (also referred to as the “bottomhole assembly” or “BHA”) at an end of the tubular member. The BHA typically includes a variety of tools and sensors that provide information relating to a variety of parameters relating to drilling operations (“drilling parameters”), behavior of the BHA (“BHA parameters”), and parameters relating to the formation surrounding the wellbore (“formation parameters”). A large number of wellbores include curved sections. A BHA used to drill non-vertical sections of the borehole often includes a steering unit to steer the drill bit along a desired direction. One type of steering unit includes a number of force application members that are moved radially outward to apply pressure on the borehole wall. A drive unit or an actuator is used to move the force application member. Formation evaluation tools used in both a BHA and in wireline tools utilize devices that include a drive unit to operate a piston to drawdown fluid from the formation. Other tools used in BHA and wireline logging tools also utilize drive units in conjunction with other devices to extract fluid from the formation for testing and analysis of the extracted fluids. Other devices in downhole tools that utilize drive units may include valves, pistons and the like. Moveable stabilizer blades, bit controllers, coring tools, mud pulse tools, and other moving components may also be configured to use drive units.
Drive units used for expanding force application members typically incorporate motor driven piston pumps that provide pressurized fluid to expand or move a piston. The pressure level is controlled by a nozzle arrangement in conjunction with pump rotational speed or torque or by a solenoid proportional valve. Certain other drive units are based on a motor-driven ball screw spindle, driving a first piston of smaller diameter to provide pressure to a larger secondary piston.
Such drive units are relatively mechanically complex and also utilize filters, flow restrictors, shut-off valves, etc. for fail-safe operations and pressure relief valves for overload protection. The complexity and components of these drive units may require frequent maintenance and be costly to manufacture. The disclosure herein provides drive units that are relatively small and address some of the above-noted problems.